For this purpose the "Sample/Reference [S/R] mode" was developed. in this mode of operation, some muons stop in an annulus of Ag ["R"] just in front of the sample, while those that pass through the hole in the annulus stop in the sample ["S"]. Both are collected into separate histograms, usually four each, for a total of 8 histograms. The separate spectra can then be analyzed together.
It is obviously not possible to have the S and R muons in exactly the same place,
so (since the firld in even the finest magnet has some spatial inhomogeneity)
it is necessary to determine whether the difference between identical
S & R materials depends on any systematic parameter such as temperature.
Click on the run-number button for one of these runs and investigate the run header information, especially the names and ordering of the data histograms. Select various Spectrum types and look at the range from 0 to 0.1 µs with 0.5 ns bins. Eventually choose Spectrum type 4 with a RRF frequency of 204 MHz and a packed bin size of 0.1 µs to display the whole time range in the RRF.
Now click on "Plot FFT" and adjust the FFT parameters and options until you get a sharp, symmetric line in the FFT, plotting the Real part of the amplitude. (Allow pop-ups in your browser!) Do this for type 4 spectra which histograms 1,3,2,4 for the Sample signal; then repeat with histograms 5,7,6,8 to see the Reference signal. Then click on a few other runs at different Ts and see if their FFTs look different.
When you know which runs you want to fit, click Zip & Download Runs at the bottom of the Run List window to bring the selected runs into your computer; then unzip the download into the directory where you want to fit them.
If you are working on bnqrexp.triumf.ca, the zip/unzip step is not required, as all runs are directly accessible in the /data/<beamline>/<year>/ directories on that host; unfortunately this is not available on the workstations in Hennings.
Use musrgui or (on bnqrexp.triumf.ca) physica ['t0', 'bkgd' and 'early' commands] to determine the t = 0 bin, background bin range and good data bin range. This is necessary because the values are poorly set in the data files! Checking one run should be sufficient. Prepare your fit-control template file, for either musrfit (.msr) or msrfit (.i), starting from another such file. There will be a single signal in each of two Spectra [S & R] and you should let each have its own initial phase, amplitude, frequency and exponential relaxation rate. Fit in the RRF of your choice.
Note: There is no real need to fit both S and R signals at the same time, since they share no common Signal parameters and are in different Spectra; it is just a bit easier to keep track of the results this way. However, you may want to try making the S frequency a function of the R frequency, like "FrqS = (1 + K)*FrqR" with K a MINUIT fit parameter; this slightly simplifies summarizing the results.
If you get frustrated trying to compose your own .I input file for msrfit, here is a template: 5111.IRRSR
You may want to try the chfit command to fit a whole series of runs
using an initial "template" file and generating a stack of results
in DB format. Ask Jess if you want to use this feature.